Information handling systems utilize high speed printers for rapidly generating printed information in a tangible form. High speed printers generally utilize xerographic or impact printing technologies. Impact printers are desirable for low cost and requested where the option to print multipart forms is desired. Printing mechanisms for impact printers generally transfers ink or other material from a print ribbon onto paper to form images on one major surface of the paper.
Continuous-form paper is usually supplied from a box in which the paper is stacked in a fan-fold pattern. The paper may be single layer or may be multi-layer to provide multi-part forms. Continuous-form paper is perforated along lateral lines to divide the continuous length into separable sheets or forms. Each of the separable sheets is rectangular and is typically 11.5 inches high by 14 and 7/8 inches wide. The paper is folded along the perforations in a zigzag manner reminiscent of oriental hand fans in which each lateral perforation is folded in the opposite direction from the preceding fold to form a stack.
Tractor drives engage a longitudinal row of holes along each edge of the paper for moving the paper longitudinally from the source box of paper, through the printing mechanism and downward toward a horizontal surface upon which it refolds in an output stack of printed, continuous forms. The tractor drives tend to distort the paper at the tractor holes in the edges of the paper so the refold stack is bowed upward at the edges. Typically, the paper length remains slightly folded along the lateral perforations after unstacking and printing and the descending paper length naturally tends to refold onto the stack at each lateral perforation in the same direction that it was originally folded.
Since the introduction of fanfold paper refolding, practitioners have faced the problem that occasionally the paper will fail to refold along the lateral perforations in the proper direction. The misfolding results in a jumble of output and for enclosed printers often results in an output paper jam and loss of data. It is known that the misfolding and jamming are related to the bowing of the stack due to the damage of the sprocket holes by the tractor drive and to the height of the paper discharge above the top of the stack and is also related to the intermittent characteristics of feeding of the paper through the printer.
The longitudinal movement of the paper through the printer is not continuous. Usually the movements is stopped as each line is printed on the sheets. Also, the paper tends to move quickly through blank lines and even more quickly through blank pages. For a very high speed paper tractor, the paper output is often accelerated so that descending paper bends as it falls into the stack and fails to properly refold onto the stack.
Also, the printer does not usually operate continuously. The output typically consists of separate reports which are sent to the printer as desired so that the printer is idle for minutes or even for hours between jobs. In addition, information handling systems tend to be idle for long periods due to schedules of working shifts, weekends and holidays. The paper in the printer may be idle with a lateral perforation in a straightened configuration so as to forget the original fold direction at the perforation; or the paper may be idle in a bent configuration and retain the bend so that it does not properly refold onto the output stack.
Once the stack is started in the proper location with the continuous length of paper refolding in the previous fan-fold directions, proper refolding tends to continue without any additional aid. However, occasionally the paper fails to refold in the desired direction which produces an unfolded jumble of printed output, and eventually applies forces to the paper moving through the tractor. The tractor tears out the sprocket holes in the paper causing the paper to stop moving through the printer.
In an effort to further prevent these occasional output jams, and to aid in starting the stack in the proper position and folding in the correct direction, some printers have utilized chains hanging vertically down from the printer frame on each major side of the descending length of folding paper. Typically the lower ends of the chains hang between 0 and 4 inches above the horizontal surface upon which the paper is refolded. At the beginning of folding, the lower chains position the paper stack symmetrically about the center between the chains. The paper pushes the lower chains outward to swing, and the swinging chains sweep against the forms to aid in refolding the continuous length of paper.
However, these swinging chains result in another mechanism for causing paper jams. The lower ends of the chains become caught in the sprocket holes along the edge of the paper or become caught between the folding layers of paper as they sweep against the folding paper. The caught chain bows the paper stack resulting in misfolds which cause paper jams. Customers, recognizing this problem, have hung small paper clips from the lower ends of the chains to extend the chains so they don't swing in order to prevent these types of jams. However this defeats the purpose of the chains. A previous printer, designated 4235, marketed by International Business Machines Corporation provided swinging chains above the highest stack height and strings with weights hanging at the lower ends of the strings. In that printer the weights hang below the horizontal surface on which the paper is stacked. The weights remain below the top of the stack and the strings don't swing against the folding paper.
U.S. Pat. No. 2,779,450 to Mecum et al. discloses "an attachment for guiding continuous prefolded forms used in connection with form stands for accounting and typewriting machines." The apparatus includes weights suspended by extra fine wire such that "the weights and string means will swing in harmony with [the movement of] said forms." U.S. Pat. No. 4,054,235 to Witcher discloses "apparatus to separate multiple sheet feeds from fanfold paper being moved from an input paper stack upwardly to a print station." U.S. Pat. No. 4,559,031 to Gysling et al. dive arresters that are suspended by chains each "having a projecting ledge . . . that upon catching the diving fold [of paper] . . . swings in reaction to the weight of the paper and releases the diving fold when the outward swinging motion of the ledge has displaced the diving fold to a position from which the fold will fall substantially into alignment with folds of previously stacked pages." U.S. Pat. No. 5,123,894 to Bergeman discloses "the lower ends of the two flexible straps 22 and 24 are secured to the ends of the narrow plate or bracket member 44." An English abstract for Japanese patent J03047773 discloses "a rod-form member 9 is swingingly suspended by wire materials 8 . . . paper 2 delivered from a paper discharge port 1a of a printer 1 abuts on the rod-form member."